The invention relates to a socket for use in testing integrated circuit packages (IC packages) in which an IC package is placed on a printed circuit substrate for testing.
As is well known in the prior art, IC packages are placed in a socket for mounting to a circuit substrate so that a heat resistance or burn-in test can be performed on the IC packages. The IC package is mounted on the socket and circuit substrate and then put into a heating furnace to test its suitability.
FIGS. 11 and 12 show prior art sockets for IC packages loading as used in such a heat-resistance test. In these sockets of FIGS. 11 and 12, a hinge part 1a is formed at one end of a base block 1 with a hinge 2a which is part of a cover 2 supported by a shaft 3. The cover 2 is rotatably supported around the shaft 3 adapted to move in the direction of opening or closing with relation to the top of the base block 1.
On the inner surface (bottom surface in the closed position) of the cover 2 along the four sides there are holding pieces 2b protruding from the cover for holding leads 100a of an IC package 100. The cover 2 is biased in the direction of being opened at all times by a spring 4 that has been provided on the shaft 3. Furthermore, a shaft 5 is provided at the opposite end of cover 2 from shaft 3 about which a latch 6 is rotatably mounted. The latch 6 has a hook 6a at its tip for engagement with the end of the base block 1 opposite the end with the hinge. A spring 7 is also provided on shaft 5 for biasing the hook 6a against the end of base block 1.
The center of the base block 1 is in the form of a rectangular frame 1d. Around this center frame 1d, a prescribed number of contacts 8 are positioned corresponding to the various leads 100a of the IC package 100 to be mounted. A lead terminal portion 8a of each contact 8 sticks out beneath the base block 1 to be connected with the circuit of the circuit substrate (not shown in the drawing) by such means as insertion or soldering.
A boss part le is provided for positioning the IC package on the surface of the base block. The boss parts 1e are positioned at four corner locations.
In accordance with the device of FIGS. 11 and 12, a lead 100a of the IC package 100 is placed on the corresponding contact 8 of the base block 1 and the outside of the lead 100a at the end of each side amongst those leads 100a on the four sides is positioned by the boss part 1e. Cover 2 is then rotated around the shaft 3 thereby closing the cover on base block 1 with holding piece 2b of the cover 2 contacting the leads 100a of the IC package. If the cover 2 is further pressed in the closed position, the hook 6a of the latch 6 engages with a claw part 1c of the base block 1 with a result that the cover 2 is fixed in the state of being closed on the top of the base block. In this state, the contacts 8 in the block are pressed into contact with the leads of the IC package 100 by the holding piece 2b of the cover 2. Contacts 8 are biased in the direction of the cover when in the closed position so that a desired contact pressure will be obtained.
After the completion of the burn-in test for the IC package, the engagement between the hook 6a of the latch 6 and the claw part 1c of the base block 1 is released and the cover 2 is returned to the open state due to the spring force of the spring 4. The IC package 100 is taken out of the top of the base block 1 and the heat resistance test is completed.
The prior art socket described above has a plurality of insulating wall members 9 upstanding from base block at a prescribed pitch interval. These insulating partition wall members are interposed between the contact members 8 having the same pitch interval as the contacts and insulate them one from another.
As more miniaturization is desired and the need for IC packages with more leads has increased, the distance between leads of an IC package has continued to decrease. This fact results in an extremely narrow pitch between leads and the need for partition/insulating walls to be extremely thin. The manufacture of these partition walls becomes extremely difficult, if not impossible, especially when they are to be formed integrally with the molding of the base block by a typical resin molding process.
For example, if the pitch of contacts 8 are set at 0.3 mm, correspondence to the pitch of the leads of the IC package and the width of the contact is set at 0.18 mm. with a clearance for the contact set at 0.02 mm., the resulting thickness of the insulating wall will necessarily become 0.1 mm, with a consequence that it will be very difficult to obtain both the size and strength that are necessary for maintaining reliable insulation.
In view of the fact, a socket design has been used in which the insulating wall protects the contacts on a partial basis as is shown in FIG. 12. The design, however, can suffer from short-circuiting phenomena and "cross-talks" between the neighboring contacts especially in the case where the IC leads are at narrow pitch. Additionally, the conventional construction, as described earlier, tends to make it easy for the noise to get into the electric signal that flows to the contacts because of its very structure.
Also, the prior art socket has the holding piece for the IC package integrally formed on the inner surface of the cover which engages the contact in an arc-shaped movement along with the rotary movement thereof. That is, the holding piece will move in an arc-like manner as compared with the IC lead being on a flat plane so that the rotary hinge side of the cover first contacts the leads followed by the contact of the holding piece at the rotary tip side with the lead.
Consequently, the holding of the holding pieces with the leads as a whole is staggered and uneven; and there are time differentials in said holding of the leads. This fact also provides an unsatisfactory possibility of a contact between IC leads and socket contacts.
Still further, the cover in the prior art socket tends to open suddenly when the latch is released after the completion of the IC package test which results in the tendency of the IC package to quickly "jump out" (move upward) in some cases. This can cause damage to the IC package.